In the existing pixel circuit, an N-type thin film transistor is typically used as a drive transistor of a light-emitting diode, but a drift in characteristic voltage (e.g., threshold voltage) of the drive transistor tends to result in a deviation in display brightness of a panel, a failure to write a data signal and other abnormal display phenomena. With a 2T1C pixel circuit illustrated in FIG. 1, in a signal write phase, a SCAN2 signal is applied to a gate of an MOS transistor M2 to turn on transistor M2, and after transistor M2 is turned on, a DATA signal is provided to a node N1 to charge a storage capacitor Cst while turning on a drive transistor M1, which generates a drive current to cause an Organic Light-Emitting Diode (OLED) between a first power supply PVDD and a second power supply PVEE to emit light. The drive transistor M1 in the pixel circuit as illustrated in FIG. 1 provides the organic light-emitting diode with the drive current IOLED as represented in Equation 1:
                                          I                          O              ⁢                                                          ⁢              L              ⁢                                                          ⁢              E              ⁢                                                          ⁢              D                                =                                    1              2                        ⁢            μ            ⁢                                                  ⁢                          C              OX                        ⁢                          W              L                        ⁢                                          (                                                      V                    GS                                    -                                      V                    TH                                                  )                            2                                      ;                            (                  Equation          ⁢                                          ⁢          1                )            
In Equation 1, μ represents carrier mobility, COX represents a gate oxide capacitance per unit area of the drive transistor M1, L represents a channel length of the drive transistor M1, W represents a gate width of the drive transistor M1, VGS represents gate-source voltage of the drive transistor M1, and VTH represents threshold voltage of the drive transistor M1. As is apparent from Equation 1, the value of the drive current IOLED is dependent upon the gate-source voltage VGS and the threshold voltage VTH of the drive transistor M1. When the thin film transistor is turned on for a long period of time, the threshold voltage of the thin film transistor tends to vary, which is referred to as a threshold drift, and the threshold drift of the drive transistor may result in non-uniform brightness of light emission by the OLED. If there is instable voltage across the gate and the source of the drive transistor after the control signal is provided, the generated drive current may also be influenced thus resulting in non-uniform light emission by the OLED.
Thus, there is the problem in the prior art of non-uniform light emission by the OLED due to the threshold voltage drift of the drive transistor or the instable voltage across the gate and the source of the drive transistor.